Technical Field
The invention relates to a resonant converter, and particularly relates to a multiphase parallel resonant converter and a control method thereof.
Related Art
LLC series resonant converter (LLC-SRC) not only has a simple structure, but also has a plurality of unique advantages, for example, a primary side switches may implement zero voltage switching (ZVS) within a full load range, and a secondary side rectifier switches may implement zero current switching (ZCS), and a wide range input voltage variation can be followed by controlling a narrow frequency variation. However, since a secondary side of the resonant converter does not have a filter inductor, ripple of an output current is quite large, which influences a service life of an output filter capacitor, and such disadvantage is more obvious in application of a large current output. In order to satisfy a ripple index of the output voltage and the output current, a multiphase LLC-SRC interleaving parallel method/technique can be adopted to overcome the aforementioned disadvantage. The interleaving parallel method refers to that frequencies of control signals of switch tubes in circuit units operated in parallel are the same, though phase angles thereof are interleaving. After the resonant converters are connected in parallel, besides that a new power supply module composed of multi-channel interleaving parallel units is constructed, a redundant parallel power supply system is also constructed.
However, when resonant parameters of the parallel resonant converters are different, direct current (DC) gain curves of various phases thereof are inevitably different, and equivalence of output gains of a two-phase resonant converter and current-balancing thereof at arbitrarily same switch frequency cannot be guaranteed. Moreover, when a load current of the parallel resonant converter is changed, the gain of the two-phase resonant converter is also varied, and such gain variation leads to output voltage variation of the two-phase resonant converter, such that accuracy of an output voltage of the power supply system deviates from/is inconsistent with requirement of electric equipment. Therefore, a control method adapted to the parallel resonant converter has to be developed, and by which current-balancing of the parallel resonant converter is achieved, and the output voltage thereof satisfies the requirement of the electric equipment.